1. Field of the Invention
The present invention relates to a defect inspection apparatus of a chip comparison inspection method, which automatically detects a defect of a semiconductor wafer, and a defect inspection method.
2. Description of the Related Art
In recent years, wiring rules have been becoming minute with the innovation of semiconductor technology, and the demand for detecting a defective chip with high accuracy at high speed has been growing in a semiconductor wafer inspection apparatus.
Accompanying this, the automation of a semiconductor wafer inspection apparatus using a microscope has been advancing, and an AF (automatic focusing) function for automatically achieving focus on an observation object has become an essential function. The performance of the AF function included in such an apparatus plays a very important role in improvements in, so-called, an inspection throughput (inspection efficiency per unit time).
For example, an semiconductor wafer automatic defect inspection apparatus of a chip comparison inspection method makes a matching (pattern matching) between a pattern of a normal chip verified beforehand and that of a chip to be inspected by taking advantage of the fact that a number of identical pattern chips are aligned and formed on a semiconductor wafer. If the apparatus determines that the patterns mismatch, it judges that an abnormal condition occurs in the chip to be inspected, and analyzes the contents of the abnormal condition.
With this automatic defect inspection apparatus, the AF is executed respectively when the pattern image of the normal chip is recognized, and when the pattern image of the chip to be inspected is captured. Therefore, the apparatus requires an AF operation time by the amount of time of the AF. Additionally, if focusing accuracy is poor, and if the image of the normal chip or the chip to be inspected becomes, so-called, defocused, the apparatus can erroneously judge the normal chip as an abnormal chip when making the pattern matching.
In the meantime, as a technology for improving AF performance such as a focusing speed and focusing accuracy, for example, Japanese Patent Publication No. H06-165019 discloses an automatic focusing apparatus switching a calculation method of a defocusing amount used to determine the focusing of AF control according to the luminance of a sample. Furthermore, Japanese Patent Application Laid-open No. H11-84228 discloses an automatic focus adjustment apparatus switching an algorithm of AF control according to brightness, which is an observation condition.